Test: Alternator vs. no alternator = 10% MPG gain @ 70 km/h

[HypermilerAX]

At how much would you estimate the gain with the belt on but the electrical load at zero ? 8 or 9% ?

[Xist]

Originally Posted by MetroMPG

Agreed 100%!

Thus the advice that for this to be financially workable in most cases, "a supply of free or cheap batteries" is required.

Don't people usually switch to deep-cycle batteries when they do this?

[hotrodfeguy]

i think a gel cell would be the way to go

[California98Civic]

Originally Posted by HypermilerAX

At how much would you estimate the gain with the belt on but the electrical load at zero ? 8 or 9% ?

Depends on the car, but most of the drag on the engine definitely comes from electrical load, not the free wheeling pulley and belt.

[RdRnr]

I drive too far to do without an alternator. And my drive home is at night so I need the lights on. I could do a switch.

Ideally, a 3-position switch: Charge, No Charge, and Auto.

Auto position would do as has been discussed: charge when brakes are applied. I would add to that, charge if battery gets below some voltage and charge if throttle is below some position. Add a switch for throttle position and a voltage comparator. Adjust switch position and voltage for best results, whatever that is. Shouldn't be too hard to do.

And then I guess I would force Charge 10 mins from home to make sure I can start the next day? Or, better, connect battery to a charger during the night.

[orange4boy]

Full charging is mandatory for lead acid. A few minutes of car charging will not keep a battery charged. They must have a full charge or they sulphate and die a premature death. That takes a long slow tapered charge to achieve. At home with an automatic charger

My take on this is different than Metrompg. I think it does pay for itself if you buy a good battery. Treated Properly, a deep cycled battery will last as long or longer than an average normally used battery and ten percent better FE adds up quickly. Optima yellow or blue top can be deep cycled more times than flooded due to higher lead purity. I have a set of d31 that are ten years old and they still outperform new series 27 deep cycles on my high amp electric motorcycle. I killed two sets of Costco deep cycles but these oldies are still kicking. They are regularly cycled to 40%.

I'm going to disable the DC-DC on the insight soon to try grid powering on that car. I may even be able to a-b-a test as I now live (ack) in the Fraser Valley. Hybrids should get an even bigger improvement than regular cars due to their hungrier electronics, electric steering, etc.

[Nerys]

I have discovered anecdotally that as long as you use quality deep cycle or agm's and don't go below 50% you get many many years life out of them. enough that you can't tell the difference between just using it as a starter battery.

1 decent unit will run my car for a week so my plan is to use 2 so neither goes below 50% and charge it up once a week.

daily in the winter since the blower and headlights will get far more usage.

[orange4boy]

Lead acid batteries actually last longer if they are gently used. (50% discharge or less) Since an un-cycled battery may require replacing every few years anyway, why not get a deep cycle one for a little more money that will last 3 to 4 times as long. (yellow top Optima)

Nerys, You should always keep lead acid batteries fully charged. Even leaving one even partially discharged overnight is not a good idea. Sulfation happens quickly and permanently damages the battery. There are ways to desulfate but they require a special device and do not restore batteries completely if at all.

[Nerys]

orange4boy I have NO doubt your 100% correct but I simply have not noticed a shortening in lifespan as a result. I have leads that I regularly discharge to 40-50% SOC 5+ years old and they still work just fine.

the amount of fuel I will save in 4-5 years of life far far far far outweights the cost of the batteries so I don't mind.

I also plan to add a solar panel to the roof (30watt) amorphous so works in low light too. in the summer I expect I won't even have to plug the car in. the 10 hours it sits in the parking lot it will get back 300 watt hours of power. less than I will use driving to and from work in theory.

[California98Civic]

Originally Posted by Nerys

I also plan to add a solar panel to the roof (30watt) amorphous so works in low light too.

Thanks for that bit of tech info.